The present invention relates to a contact drop wire for an electric warp stop having a chamfered drop wire head.
The contact drop wire for the known electric warp stop is held in a specific position by the warp thread during the weaving operation. If the warp thread tears, the drop wire falls on the contact rail and, due to its shape, closes the electric circuit between the inner and outer part of the contact rail. The current flowing through it serves to turn off the weaving machine. Imperfect fabrics are avoided with these measures.
The shape of the currently widespread contact drop wires is largely internationally standardized. Depending on the system of the drawing-in machines that are used, the angle .alpha.(see FIG. 1) is fixed at 30.degree. or 37.degree.. This large slope has been fixed a long time ago which assumes that it suffices to reliably and rapidly close the electric circuit between the inner and outer part of the contact rail. However, it has been demonstrated more and more that this requirement is not adequately met. Especially for weaving machines with weft insertion numbers exceeding 600 per minute, the contact does not, with any degree of frequency, effect a shutting down of the weaving machine fast enough. In contrast, experience shows that the drop wire slope does not effect a sufficiently rapid sliding on the contact rail in order to reliably close the electric current. In particular, upon soiling of the warp thread due to the abrasion of the sizing, the sliding of the drop wire and is impeded the transition resistance between the drop wire and contact rail increases.
To remedy this problem, the drop wire could be designed to slide faster on the incline by the provision of a steeper angle so as to also increase the contact pressure with respect to the contact rail. Unfortunately, this solution is not commercially feasible. Most of the larger weaving mills pull in the warp threads automatically and, in particular, also by means of the drop wires. These machines are arranged now in such a manner that the drawing-in means are adapted precisely to the drop wire incline of 37.degree. or 30.degree.. As apparent from FIGS. 2 to 4 of the accompanying drawings, a modification in the angle would change the position of the drop wire. This, however, is not Permissible. Either the drop wire or the automatic drawing-in machine would be damaged. Normally retrofitting the drawing-in machne is not a solution, since othewise the old shapes of drop wire that are in circulation in the hundreds of millions could no longer be manufactured. In particular, drawing-in mills, which work by job orders, would never proceed in such manner.